Hydrogenation catalysts

ABSTRACT

A hydrogenation catalyst which is sulfur tolerant and which includes from about 0.1 to about 1 percent platinum by weight and from 0.2 to about 2 percent by weight palladium on a predominantly theta alumina carrier. Also disclosed is a process for the manufacture and use of the hydrogenation catalyst.

RELATED APPLICATIONS

[0001] This is a divisional application of application Ser. No.09/362,408, filed Jul. 28, 1999.

BACKGROUND OF INVENTION

[0002] The field to which this invention pertains is hydrogenationcatalysts, and more particularly, sulfur tolerant, aromatichydrogenation catalysts and a process for their use.

DESCRIPTION OF THE RELATED ART

[0003] There is today a significant need in the petroleum industry fornon-aromatic solvents, including liquid hydrocarbons which boil in therange of about 200 to 1100° F. Such products include, for example,aviation turbine fuel, diesel fuel, solvents, white oil, lube oil andthe like. Products in this boiling range are conventionally produced bythe hydrotreating and/or hydrocracking of various refinery feed streams,boiling in and above the desired product range. While hydrotreating andhydrocracking operations generally affect substantial partialhydrogenation of polynuclear aromatics, the resulting products stillcontain a relatively high percentage of monoaromatic hydrocarbons and asubstantial amount of sulfur. Further hydrogenation of these products isdesired in many cases to produce acceptable solvent products and to meetspecifications for jet fuels and other such final products.

[0004] Other conventional hydrogenation applications include thehydrogenation of benzene to cyclohexane. One process for the productionof cyclohexane comprises contacting a mixture of benzene, cyclohexaneand hydrogen under hydrogenation conditions in the presence of a GroupVI and Group VIII metal hydrogenation catalyst, such as is disclosed inU.S. Pat. No. 3,622,645. See also U.S. Pat. No. 3,869,521 whichdiscloses a transition metal catalyst useful for the conversion ofbenzene to cyclohexane.

[0005] The hydrogenation of unsaturated hydrocarbons, particularlyaromatic hydrocarbons, to corresponding saturated hydrocarbons usingplatinum and/or palladium catalysts is disclosed in U.S. Pat. No.3,637,484. In this patent, platinum and/or palladium are depositedselectively by cationic exchange upon a silica/alumina co-gel orcopolymer, which in turn is dispersed in a large pore alumina gelmatrix.

[0006] U.S. Pat. No. 3,674,888 discloses a process for selectivelyhydrogenating unsaturated hydrocarbons in their liquid phase utilizingpalladium on an alumina catalyst. The catalyst is the product resultingfrom contacting alumina agglomerates of a specific surface area withsteam, admixing the agglomerate with a palladium compound and calciningthe resulting mixture.

[0007] A significant problem that can occur with platinum and/orpalladium catalysts is that they can be poisoned by sulfur compoundsthat may be present in the feed stream. A platinum and palladiumcatalyst for the selective hydrogenation of aromatics and olefins withsome tolerance for sulfur and nitrogen is disclosed in U.S. Pat. Nos.4,049,576 and 3,943,053. These patents teach a catalyst containing from0.2 to 1 percent by weight of each of platinum and palladium impregnatedon an inert carrier, preferably a high surface area, gamma alumina.

[0008] Another high surface area gamma alumina-based catalyst useful forthe hydrogenation of unsaturated hydrocarbons is disclosed by U.S. Pat.No. 3,674,888. Other high surface area catalysts, preferably using agamma alumina carrier, are disclosed in U.S. Pat. No. 4,713,363. Seealso U.S. Pat. No. 4,952,549.

[0009] In addition to alumina-based carriers, silica-alumina carriersonto which noble metals, such as platinum or palladium, are impregnatedfor the hydrogenation of petroleum feed streams are disclosed, forexample, in U.S. Pat. No. 3,637,484. A catalyst with sulfur tolerancefor the hydrogenation of aromatics, wherein the carrier comprises asurface-modified alumina/silica support, onto which noble metals havebeen impregnated, is disclosed in WO 98/35754. See also U.S. Pat. Nos.3,461,181, 3,859,370 and 4,251,392.

[0010] Other catalyst containing palladium and/or platinum secured oninert alumina and/or silica carriers are disclosed in U.S. Pat. Nos.2,911,357, 3,173,857, 3,271,327, 3,280,041, 3,549,720, 3,759,823 and3,703,461, GB 1,501,346 and WO 98/35,754.

[0011] While some of these catalysts are useful for hydrogenatingvarious unsaturated feed streams, there is still a need for improvedhydrogenation catalysts.

[0012] In addition, prior art noble metal catalysts are stillsusceptible to poisoning from sulfur and/or nitrogen present inconventional feed streams. Thus, improved catalysts which have atolerance for sulfur are also needed.

[0013] It is therefore an object of the invention to provide a novelhydrogenation catalyst.

[0014] It is another object of the invention to provide an improvedhydrogenation catalyst for the conversion of aromatics in a feed stream,where the catalyst has high activity.

[0015] It is another object of the invention to provide an improvedhydrogenation catalyst for the conversion of benzene to cyclohexane,where the catalyst has high activity and selectivity.

[0016] It is another object of the invention to provide an improvedhydrogenation catalyst with a tolerance for low to medium levels ofsulfur in a feed stream.

[0017] It is another object of the invention to provide an improvedhydrogenation catalyst containing platinum and palladium on a transitionalumina carrier.

[0018] It is another object of the invention to provide an improvedhydrogenation catalyst for the removal of aromatics from a feed stream,where the catalyst comprises one or more noble metals, preferablyplatinum and palladium, placed on a predominantly theta alumina carrier.

[0019] These and other objects of the invention are obtained by theproduct and process of the present invention.

SUMMARY OF THE INVENTION

[0020] The invention is directed to an improved hydrogenation catalystfor the hydrogenation of aromatics and other unsaturated compounds in ahydrocarbon feed stream, which boils in the range from about 200 toabout 1100° F., and which may contain up to about 150 ppm of totalsulfur. The catalyst of this invention includes from about 100 ppm toabout 5 percent by weight of each of platinum and palladium, preferablyfrom about 0.1 to about 1.0 percent platinum and from about 0.2 to about2.0 percent palladium. The preferred molar ratio of platinum topalladium in the catalyst is from about 1 to 4 to about 1 to 7. Thecarrier for the catalyst is an inert alumina carrier, wherein thealumina preferably comprises at least about 50 percent theta (or delta)alumina, with the remaining portion of the carrier being preferablyalpha alumina, preferably from about 1 to about 40 percent. Minoramounts of other transition aluminas may also be present.

[0021] The invention is also directed to a process for the hydrogenationof feed streams containing aromatic or other unsaturated hydrocarbonsand less than about 150 ppm of sulfur in contaminants by use of theabove-described catalyst.

[0022] The invention is also directed to a process for the production ofthe above-referenced hydrogenation catalyst.

DETAILED DESCRIPTION OF THE INVENTION

[0023] The catalyst of the invention is preferably a bimetallic, GroupVIII catalyst, wherein the Group VIII elements are preferably platinumand palladium, which are impregnated on an inert catalyst support orcarrier. While other noble metals may be used for the catalyst, it hasbeen discovered that superior hydrogenation catalysts are produced whenplatinum and palladium are utilized.

[0024] The catalyst support or carrier for the platinum and palladium ispreferably a medium to low surface area alumina carrier, more preferablya predominantly theta (or delta) alumina carrier. Preferably the surfacearea of the carrier is from about 30 to about 150 m²/g, more preferably30-110 m²/g, most preferably from about 60 to about 100 m²/g. Theta (ordelta) alumina comprises at least about 50 percent of the carrier,preferably at least about 60 percent. In order to maintain a relativelylow surface area of less than about 150 m²/g for the catalyst, up toabout 40 percent of the carrier may also constitute an alpha alumina.Any combination of theta (or delta) alumina carrier and alpha aluminacarrier which produces a carrier with a surface area within thepreferred range is within the scope of the invention. Minor amounts ofother transition aluminas may also be present in the carrier.

[0025] Various transition states of alumina are formed during thermaltreatment of hydrated alumina. Their specific transition state isdefined based on a number of considerations, including crystalstructure, method of formation and surface area. At least seventransition forms of alumina are recognized, as discussed in Kirk-Othmer,Encyclopedia of Chemical Technology, Second Edition, Volume 2, pages48-58 (1963). Three of these forms, chi, eta, and gamma, are poorlycrystallized and three, kappa, delta and theta, are relatively wellcrystallized. A seventh form, rho alumina, may be considered amorphous.(Some authorities have asserted that rho alumina is also crystallized,but more poorly crystallized than gamma alumina.)

[0026] The specific surface area of the chi and eta forms of transitionalumina are relatively high, ranging from 250 to 500 m²/g with thespecific surface area of gamma alumina ranging from 150-300 m²/g. Incontrast, the surface areas of kappa, theta and delta alumina aresignificantly lower with the surface area of delta and theta aluminagenerally in the range of about 60 to 100 m²/g. The specific surfacearea of alpha alumina is lower still, generally less than about 30 m²/g.Because of its relatively high surface area and ease of formation, gammaalumina has been frequently utilized as a carrier of choice for certainnoble metal hydrogenation catalysts, such as those disclosed in U.S.Pat. Nos. 3,280,041, 4,049,576, 3,943,053 and 4,713,363.

[0027] Besides surface area, additional differences exist among thevarious forms of transition alumina as disclosed more completely onTable 3 of the article from Kirk Othmer which is referenced above. Forexample, the temperature needed to form the delta (and theta) forms oftransition alumina is significantly higher (900-1000° C.) than thatwhich is used to form the rho, eta and gamma forms of transition alumina(200-600° C.).

[0028] Because the specific surface area and crystal structure of thetaand delta alumina are so similar, it is often difficult to distinguishbetween these two forms of alumina. Therefore, for purposes of thisinvention, all references to theta alumina also include delta alumina.

[0029] It has been surprisingly discovered that improved palladium andplatinum catalysts for the hydrogenation of aromatic feed streamscontaining sulfur contaminants can be prepared from theta aluminacarriers. This is surprising as the surface area of a carrier usingtheta alumina is significantly less than that of a conventional gammaalumina carrier used for the hydrogenation process as disclosed, forexample, in U.S. Pat. No. 4,049,576.

[0030] Any reasonable method for depositing the platinum and thepalladium on the referenced carrier can be used. In one preferredembodiment to impregnate the carrier with platinum and palladium, anaqueous solution, preferably consisting of chloroplatinic acid andpalladium chloride, such as is supplied by Colonial Metals, is firstprepared. The amount of chloroplatinic acid and palladium chloridedissolved in an aqueous solution is the amount sufficient to provide afinal calcined catalyst containing from 100 ppm to about 5.0 percent byweight each of elemental platinum and palladium metals. Preferably, theplatinum present in the catalyst comprises from about 0.1 to about 1.0percent by weight and the palladium present in the catalyst comprisesfrom about 0.2 to about 2.0 percent by weight. In a more preferredembodiment, the platinum comprises from about 0.1 to about 0.5 percentby weight and the palladium from about 0.2 to about 1.0 percent byweight of the catalyst. The preferred molar ratio of the platinum to thepalladium in the catalyst is from about 1 to 3 to about 1 to 9,preferably from about 1 to 4 to about 1 to 7.

[0031] Because of the use of platinum and/or palladium chlorides inpreparing the catalyst, the finished catalyst may also contain residualquantities of chlorides, from about 0.1 up to about 2 percent by weight.Surprisingly, the presence of chlorides in this range in the finalcatalyst may actually improve the overall performance of the catalyst.

[0032] To prepare the catalyst, the alumina carrier, which comprisespredominantly theta alumina, is first prepared. To form the carrier aprecursor material, such as boehmite powder, is first mixed with waterand, if necessary, a suitable peptizing agent, such as an acid, toimprove its mechanical strength. The carrier is then dried at lowtemperature to evaporate water and is then calcined at a temperaturefrom about 1500 to about 2500° F. (816 to about 1371° C.) to form thetaalumina. The composition of the alumina is confirmed by conventionalcharacterization procedures, such as x-ray diffraction. The aluminacarrier may include, in addition to theta alumina, various amounts ofalpha alumina. Preferably, the theta alumina comprises at least about 50percent of the carrier, more preferably, at least about 60 percent, withthe remaining portion being alpha alumina, preferably from about 1 toabout 40 percent, by weight. Minor amounts of other aluminas may also bepresent, such as gamma alumina, but in amounts less than about 5percent. Heat treatment of the carrier reduces the surface area of thecatalyst preferably to a range from about 30 to about 150 m²/g, morepreferably from about 50 to about 110 m²/g, most preferably about 60 toabout 100 m²/g with a pore volume in the range of about 0.3 to about 0.7cc/g. Any combination of theta alumina carrier and alpha alumina carrierwhich produces a carrier within the required surface area is within thescope of the invention.

[0033] The carrier can be formed in any conventional shape such as apowder, pellet, extrudate or sphere. Preferably, the carrier is formedinto an extrudate of small size, preferably less than about 0.25 inch(0.6 cm.) in diameter.

[0034] Once the predominantly theta alumina carrier is formed, theplatinum and palladium components are added. Any conventional processfor impregnating a carrier with platinum and palladium is within thescope of the invention. In one embodiment, the carrier is impregnatedwith a solution of the chloroplatinic acid and palladium chloride. Theamount of chloroplatinic acid and palladium chloride present in thesolution depends on the level of palladium and platinum loadings desiredon the predominantly theta alumina carrier. The wet catalyst is coveredand left to absorb the materials for an extended period of time,preferably from about 2 to about 24 hours. The catalyst is then allowedto dry at ambient temperature for about 24 hours.

[0035] The catalyst may also be prepared by an incipient wetnessprocess.

[0036] The dried catalyst is then calcined at a temperature up to about500° C. (932° F.) for about 2 hours. At the conclusion of the calciningoperation, the catalyst is ready for reduction. Reduction isaccomplished by heating the catalyst composition in the presence ofhydrogen at a temperature between about 500° F. (260° C.) and about 842°F. (450° C.) at a pressure of about 0 to about 2,000 psig for 3 hours.Alternatively, the catalyst may be reduced in situ by passing hydrogengas at the above-referenced temperatures and under the above-referencedpressure.

[0037] It has been discovered that the catalyst prepared by theabove-described process is “sulfur tolerant.” “Sulfur tolerant” meansthat the catalyst will not substantially deactivate during thehydrogenation reaction with a certain level of sulfur present in thefeed stream. This sulfur tolerance means that the hydrogenation catalystof the invention is utilizable in conventional hydrogenation procedureswherein the feed streams contain modest levels of sulfur (less thanabout 150 ppm of total sulfur in the form of sulfur compounds) andremains active for a conventional length of time, i.e., the catalyst hasa reasonable life cycle. The length of time that the catalyst of theinvention retains good activity varies, depending on the specific feedstream utilized and other variables well recognized in the art.Notwithstanding, the catalyst of the invention is at least as, or more,sulfur tolerant as conventional sulfur tolerant hydrogenation catalystsused for the referenced hydrogenation process as where cracking andshift in boiling point are undesirable.

[0038] The catalyst of this invention preferably acts as a hydrogenationcatalyst for the hydrogenation of unsaturated components in a liquidhydrocarbon stream. These feedstocks usually, or at least often, containrelatively high percentages of olefins and mononuclear and polynucleararomatics which require further hydrogenation. The catalyst of thisinvention can also serve as a hydrogenation catalyst for aromatics,olefins and diolefins and for the hydrogenation of benzene tocyclohexane. The presence of sulfur compounds in many of thesefeedstocks often complicates the hydrogenation process by poisoning themetal catalyst used for hydrogenation. The catalyst of the presentinvention is tolerant of reasonable levels of sulfur or sulfur compoundsin the feed stream, as discussed above.

[0039] It has been surprisingly discovered that a catalyst formed by theabove-referenced process using predominantly theta (or delta) aluminacatalyst perform better than conventional platinum and palladiumcatalyst deposited on a gamma alumina carrier as disclosed, for example,in U.S. Pat. No. 4,049,576.

EXAMPLES

[0040] The following examples describe the invention in more detail.Parts and percentages are by weight unless otherwise designated.

Example 1

[0041] A conventional alumina carrier in extrusion was formed by mixingboehmite powder with water and, if needed, by adding a peptizing agentto improve its mechanical strength. The carrier was extruded into aconventional shape with a diameter of about {fraction (1/20)} in. Theformed carrier was dried at a low temperature to evaporate water andthen calcined with the temperature ramped to a final temperature of 1500to 2500° F. (816 to about 1371° C.) and kept at the final temperaturefor 2-30 hours to produce a carrier comprised 96 percent theta aluminaand 4 percent alpha alumina. Confirmation of the structure of thecarrier was provided by x-ray diffraction. The carrier was thenimpregnated using an incipient wetness technique using a solution ofhexachloroplatinic acid and palladium chloride of sufficientconcentration to result in the platinum and palladium loadingsreferenced below. The catalyst carrier was left covered in the solutionand allowed to soak for 18 to 24 hours. The catalyst was then uncoveredand allowed to dry at ambient temperatures for about 24 hours. The driedcatalyst was calcined in a furnace with the temperature raised in 10° C.increments and held for two hours at each of the following temperatures:140° C., 300° C. and 500° C.

[0042] The catalyst contained 0.20 percent by weight platinum, 0.57percent by weight palladium and 0.45 percent by weight chloride. Thecarrier for the catalyst had a surface area of 84 m²/g and a pore volumeof 0.44 cc/g as shown in Table 1.

[0043] The performance of the catalyst was tested for hydrogenation ofaromatics in a HCLGP/LGO light gas oil blend containing 25 weightpercent total aromatics, 50 ppms S, 2 ppm WN with the results shown inTable 1.

Example 2

[0044] The same procedure of Example 1 was followed except the steps ofsoaking and room temperature drying were omitted. The catalyst contained0.19 percent platinum, 0.56 percent palladium, and 0.39 percent chlorideby weight.

Comparative Example 3

[0045] The carrier used was a gamma alumina formed and calcined byconventional procedures. That the carrier was predominantly gammaalumina was confirmed by x-ray diffraction. The surface area of thecarrier was 205 m²/g with a pore volume of 0.61 cc/g. The otherprocedures performed for preparing the catalyst were the same as inExample 1. The catalyst contained 0.21 percent platinum and 0.59 percentpalladium.

Example 4

[0046] A larger pore carrier was prepared with the addition of aburn-out material which was calcined using the procedures of Example 1.It contained approximately 63 percent theta alumina and 37 percent alphaalumina. The impregnation and calcination procedures were the same as inExample 2. The catalyst contained 0.19 percent by weight platinum, 0.585percent by weight palladium and 0.38 percent by weight chloride.

Comparative Example 5

[0047] A catalyst was produced according to the procedure disclosed inU.S. Pat. No. 4,049,576, Example 1. The carrier extrusion was a gammaalumina prepared as in Comparative Example 3. The concentration of theplatinum and palladium on the carrier was 0.19 percent and 0.59 percentby weight respectively.

Catalyst Activation and Performance Tests

[0048] 12.3 g by mass of each catalyst of each Example was loaded into areactor, dried at 300° C. for two hours under a nitrogen flow. Thereactor was pressurized with hydrogen to 550 psig pressure. The catalystwas thus reduced at 300° C. with hydrogen for 3 hours and cooled to 260°C. The reduced catalyst was tested for hydrogenation of aromatics in alight gas oil feed containing 25 weight percent total aromaticcompounds, about 3.8 percent poly aromatics, 50 ppm WS and 2 ppm WN. Thetests were run at 550 psig and 550° F., H₂/HC of 2000 scf/bbl and anLHSV of 1.2 l/l/hr.

[0049] The test results of these samples are summarized in Table 1. Thecatalyst with the highest aromatics conversion, i.e., the least amountof aromatics remaining in the product was the most active. As is provedby these examples, the catalyst of Examples 1, 2 and 4 using thepredominantly theta alumina carrier were significantly more active thanthe gamma alumina carrier catalysts of Comparative Example 3 orComparative Example 5 produced by the process disclosed in U.S. Pat. No.4,049,576.

[0050] The principal preferred embodiments and modes of operation of thepresent invention have been described in the foregoing specification.The invention which is intended to be protected herein, however, is notto be construed as limited to the particular forms disclosed as theseare to be regarded as illustrative rather than restrictive. Inparticular, the application of the catalyst of this invention isspecifically not limited to the hydrogenation of aromatics inhydrocarbons. Variations and changes may be made by those skilled in theart without departing from the spirit of the invention. TABLE 1 % TotalCarrier Aromatics Pore Palladium Platinum Remaining in Surface Volume, %Pd on % Pt on Product After Example Type Area, m²/g cc/g Source CatalystSource Catalyst Treatment 1 96% theta, 84 0.44 palladium 0.57hexachloroplatinic 0.20 0.3 4% alpha chloride acid alumina 2 96% theta84 0.44 palladium 0.56 hexachloroplatinic 0.19 0.2 4% alpha chlorideacid alumina Compar- gamma 205  0.61 palladium 0.59 hexachloroplatinic0.21 1.4 ative alumina chloride acid 3 4 63% theta, 85 0.56 palladium 0.585 hexachloroplatinic 0.19 <0.1 37% alpha chloride acid aluminaCompar- gamma 205  0.61 palladium 0.59 hexachloroplatinic 0.19 3.4 ativealumina chloride acid 5

1. A process for hydrogenation of an aromatic feed stream containingsulfur comprising passing the aromatic feed stream over a hydrogenationcatalyst comprising from about 100 ppm to about 5.0 percent by weight ofeach of platinum and palladium and an inert alumina carrier, wherein thealumina carrier comprises at least about 50 percent, by weight, of atheta or delta alumina wherein the surface area of the theta or deltaalumina carrier is from 60 to about 100 m²/g.
 2. The process of claim 1wherein the sulfur comprises less than about 150 ppm by weight of thefeed stream.
 3. The process of claim 1 wherein the aromatic feed streamis predominantly benzene.
 4. A process for hydrogenation of a diolefinfeed stream containing sulfur, comprising passing the feed stream over ahydrogenation catalyst comprising from about 100 ppm to about 5.0percent by weight of each of platinum and palladium and an inert aluminacarrier, wherein the alumina carrier comprises at least about 50percent, by weight, of a theta or delta alumina wherein the surface areaof the theta or delta alumina carrier is from 60 to about 100 m²/g. 5.The process of claim 4 wherein the alumina carrier comprises at leastabout 60 percent by weight of a theta or delta alumina.
 6. The processof claim 1 wherein the alumina carrier comprises from about 1 to about40 percent by weight of an alpha alumina.
 7. The process of claim 1wherein the weight of platinum comprises from about 0.1 to about 1.0percent by weight of the catalyst.
 8. The process of claim 1 wherein theweight of palladium comprises from about 0.2 to about 2.0 percent byweight of the catalyst.
 9. The process of claim 1 wherein the weight ofplatinum comprises from about 0.1 to about 1.0 percent by weight and theweight of palladium is from about 0.2 to about 2.0 percent by weight ofthe catalyst.
 10. The process of claim 1 wherein the catalyst furthercomprises from about 0.1 to about 2 percent by weight of chloride. 11.The process of claim 1 wherein the molar ratio of the platinum to thepalladium on a mole ratio basis in the catalyst is from about 1 to 3 toabout 1 to
 9. 12. The process of claim 1 wherein the molar ratio of theplatinum to the palladium on a mole ratio basis in the catalyst is fromabout 1 to 4 to about 1 to
 7. 13. The process of claim 1 wherein thecatalyst is sulfur tolerant.
 14. The process of claim 1 wherein thecatalyst has a pore volume of from about 0.3 to about 0.7 cc/g.